In general, combustion air for engines needs to be filtered to prevent particulates, otherwise carried in the intake air stream, from reaching sensitive engine components. As a result, nearly every engine system involving combustion air includes an air cleaner assembly of some type positioned in the intake air stream.
Many air cleaner assemblies generally comprise a housing through which the air is directed during filtration or cleaning. In some systems, a removable and replaceable filter element, or a combination of such filter elements, is provided within the housing. In use, the air is directed through the filter element(s) as it moves through the housing. In time, the filter element(s) becomes occluded or loaded with a concomitant increase in restriction across the air cleaner. At an appropriate service point, the filter element(s) is removed and is either refurbished (cleaned) or replaced.
Certain very large and powerful equipment types generate unique problems with respect to air cleaner operation. Consider large earth movers, haul trucks, and other very large types of construction and mining equipment that have 500–2,000 horsepower (hp) (37.3–149.2 KW) engines.
Such equipment operates for extended periods in extremely dusty environments. Such equipment also has very large volume demands for combustion air. This means very large amounts of particle-laden air on an almost continuous basis is passing through the air cleaner system. Indeed, the typical environments of use, for example construction sites and mining sites, are sites characterized by relatively large amounts of air borne particulates of a variety of sizes and population distribution. Special heavy-duty multistage filtration units have been designed for use with such equipment. One such design has been available from Donaldson Company, Inc. of Minneapolis, Minn. under the designation SRG Donaclone™. Such products are designed for an air flow of up to approximately 1,300–4,500 cubic feet per minute (cfm) (81,000–281,000 pounds water per minute (pwm)) and are available in single or dual unit designs. In general, such arrangements are multistaged. In a first stage, a precleaner is provided for removal of up to 95% of the dirt in the air stream before it reaches the filters. Such precleaners generally operate by directing the inlet air flow through a plurality of cyclonic tubes with dust separation occurring as a result of the cyclonic air flow. Cyclonic precleaners are described, for example, in U.S. Pat. No. 5,693,109, incorporated herein by reference.
In the second stage, the air from the precleaner is directed into and through an air filter system, typically a filter system provided by two elements: an outer primary filter element and an internal secondary or safety element. The housings are generally configured so that, periodically, the primary filter (and if desired the secondary filter) can be removed and be refurbished or replaced.